Material with a hierarchical porosity comprising silicon

ABSTRACT

A material with a hierarchical porosity is described, constituted by at least two spherical elementary particles, each of said spherical particles comprising zeolitic nanocrystals having a pore size in the range 0.2 to 2 nm and a matrix based on silicon oxide, which is mesostructured, having a pore size in the range 1.5 to 30 nm and having amorphous walls with a thickness in the range 1 to 20 nm, said spherical elementary particles having a maximum diameter of 10 μm. the matrix based on silicon oxide may contain aluminium. The preparation of said material is also described.

The present invention relates to the field of materials comprisingsilicon, in particular metallosilicate materials and more preciselyaluminosilicate materials having a hierarchical porosity in the field ofmicroporosity and mesoporosity regions. It also relates to thepreparation of said materials which are obtained using the “aerosol”synthesis technique.

PRIOR ART

Novel synthesis strategies for producing materials with a porosity whichis well defined over a very broad range, from microporous materials tomacroporous materials via materials with a hierarchical porosity, i.e.with pores of various sizes, have been widely developed in thescientific community since the middle of the 1990s (G J de A ASoler-Illia, C Sanchez, B Lebeau, J Patarin, Chem Rev 2002, 102, 4093).Materials are obtained in which the pore size is controlled. Inparticular, the development of syntheses using “mild chemistry” methodshas led to the production of mesostructured materials at low temperatureby the co-existence in aqueous solution or in polar solvents ofinorganic precursors with templates, generally ionic or neutralmolecular or supramolecular surfactants. Controlling the electrostaticinteractions or hydrogen bonding between the inorganic precursors andthe template jointly with hydrolysis/condensation reactions of theinorganic precursor has led to a cooperative organization of organic andinorganic phases generating micellar aggregates of surfactants ofcontrolled uniform size in an inorganic matrix. This cooperativeself-organization phenomenon governed, inter alia, by the concentrationof the template, may be induced by progressive evaporation of a solutionof reagents in which the concentration of the template is lower than thecritical micellar concentration, which leads either to the formation ofmesostructured films in the case of deposition onto a substrate(dip-coating) or to the formation of a mesostructured powder when thesolution is atomized (aerosol technique). As an example, U.S. Pat. No.6,387,453 discloses the formation of mesostructured organic-inorganichybrid films using the dip coating technique, the same authors havingalso used the aerosol technique to produce purely silicic mesostructuredmaterials (C J Brinker, Y Lu, A Sellinger, H Fan, Adv Mater 1999, 11,7). The pores are then released by eliminating the surfactant, thisbeing carried out conventionally by chemical extraction or by heattreatment.

Several classes of mesostructured materials have been developed usingthe different natures of the inorganic precursors and the templateemployed as well as the operating conditions imposed. As an example, theM41S class initially developed by Mobil (J S Beck, J C Vartuli, W JRoth, M E Leonowicz, C T Kresge, K D Schmitt, C T-W Chu, D H Olson, E WSheppard, S B McCullen, J B Higgins, J L Schlenker, J Am Chem Soc, 1992,114, 27, 10834) constituted by mesoporous materials obtained using ionicsurfactants such as quaternary ammonium salts, having a generallyhexagonal, cubic or lamellar structure, pores of uniform size in therange 1.5 to 10 nm and amorphous walls with a thickness of the order of1 to 2 mm, has been widely studied. Subsequently, to increase thehydrothermal stability while developing the acid-basic propertiesrelative to said materials, incorporation of elemental aluminium intothe amorphous silicic framework by direct synthesis or by post-synthesisprocesses have been particularly regarded, the aluminosilicate materialsobtained having a Si/Al molar ratio in the range 1 to 1000 (S Kawi, S CChen, Stud Surf Sci Catal 2000, 129, 227; S Kawi, S C Shen, Stud SurfSci Catal 2000, 129, 219; R Mokaya, W Jones, Chem Commun 1997, 2185).The hydrothermal stability and acid-basic properties developed by suchaluminosilicates, however, did not allow them to be used on anindustrial scale in refining processes or in petrochemistry, which hassteadily led to the use of novel templates such as block copolymer typeamphiphilic macromolecules, these latter producing mesostructuredmaterials having a generally hexagonal, cubic or lamellar structure,with uniform sized pores in the range 4 to 50 nm and amorphous wallswith a thickness in the range 3 to 7 nm. Depending on the structure anddesired degree of organization for the final mesostructured material,the synthesis methods employed could take place in an acidic medium (pHapprox 1) (International patent application WO-A-99/37705) or in aneutral medium (WO-A-96/39357), the nature of the template used alsoplaying a major role. The mesostructured aluminosilicate materialsobtained have enhanced hydrothermal stability properties compared withtheir homologues synthesized using other templates, their acid-basicproperties remaining very similar (1<Si/Al<1000) (D Zaho, J Feng, Q Huo,N Melosh, G H Fredrickson, B F Chmelke, G D Stucky, Science, 1998, 279,548; Y-H Yue, A Gédéon, J-L Bonardet, J B d'Espinose, N Melosh, JFraissard, Stud Surf Sci Catal 2000, 129, 209).

Despite the great deal of work explained above aimed at improving thehydrothermal stability and acid-basic properties of mesostructuredaluminosilicate materials, they have not yet been developed on anindustrial scale, principally because their catalytic behaviour linkedto their acidity is closer to an amorphous aluminosilicate than to acrystalline zeolitic aluminosilicate. A great deal of work has thus beenundertaken to produce aluminosilicate materials having the advantages ofboth an organized mesoporous structure and those of a micro crystallineframework. Several synthesis techniques to produce mixed materials ormesostructured/zeolite composites have thus been recorded in the openliterature. A first synthesis technique consists in a first step ofsynthesizing a mesostructured aluminosilicate material using theconventional methods explained above then, in a second step,impregnating said material with a template normally used forsynthesizing zeolitic materials. A suitable hydrothermal treatmentresults in zeolitization of the amorphous walls of the startingmesostructured aluminosilicate (U.S. Pat. No. 6,669,924). A secondsynthesis technique consists of bringing a colloidal solution of zeoliteseeds into the presence of a template normally used to create amesostructuration of the final material. Production of an inorganicmatrix with an organized meosporosity and growth in that matrix ofzeolite seeds to obtain a mesostructured aluminosilicate material havingcrystalline walls are simultaneous (Z Zhang, Y Han, F Xiao, S Qiu, LZhu, R Wang, Y Yu, Z Zhang, B Zou, Y Wang, H Sun, D Zhao, Y Wei, J AmChem. Soc, 2001, 123, 5014; Y Liu, W Zhang, T J Pinnavaia, J Am ChemSoc, 2000, 122, 8791). A variation of those two techniques consists ininitially preparing a mixture of aluminium and silicon precursors in thepresence of two templates, one of which can generate a zeolitic system,the other of which can generate mesostructuration. This solution thenundergoes two crystallization steps using variable hydrothermaltreatment conditions, a first step which results in the formation of themesoporous structure with an organized porosity and a second step whichresults in zeolitization of the amorphous walls (A Karlsson, M Stocker,R Schmidt, Micropor Mesopor Mater 1999, 27, 181). All of those synthesismethods suffer from the disadvantage of damaging the mesoporousstructure and thus losing its advantages in the case in which growth ofthe zeolite seeds or wall zeolitization is not completely controlled,which renders such techniques difficult to carry out. It is possible toavoid that phenomenon by directly producing mesostructured/zeolitecomposites. This is achieved by heat treating a mixture of a solution ofzeolite seeds and a solution of mesostructured aluminosilicate seeds (PProkesova, S Mintova, J Cejka, T Bein, Micropor Mesopor Mater, 2003, 64,165), or by growing a layer of zeolite on the surface of apre-synthesized mesostructured aluminosilicate (D T On, S Kaliaguine,Angew Chem Int Ed, 2002, 41, 1036). From an experimental point of view,in contrast to the dip coating or aerosol techniques described above,the aluminosilicate materials with a hierarchical porosity as definedare not obtained by progressive concentration of inorganic precursorsand template(s) in the solution in which they are present, but areobtained conventionally by direct precipitation in an aqueous solutionor in polar solvents by adjusting the value of the critical micellarconcentration of the template. Further, synthesis of such materialsobtained by precipitation necessitates a maturation step in an autoclavesince they may be found in the supernatant. The elementary particlesnormally obtained are not regular in shape and are generallycharacterized by a size that is generally between 200 and 500 nm,sometimes more.

SUMMARY OF THE INVENTION

The invention concerns a material with a hierarchical porosity,constituted by at least two spherical elementary particles, each of saidspherical particles comprising zeolitic nanocrystals having a pore sizein the range 0.2 to 2 nm and a matrix based on silicon oxide, which ismesostructured, having a pore size in the range 1.5 to 30 nm and havingamorphous walls with a thickness in the range 1 to 20 nm, said sphericalelementary particles having a maximum diameter of 10 μm. Said matrixbased on silicon oxide optionally further comprises at least one elementX selected from the group constituted by aluminium, titanium, tungsten,zirconium, gallium, germanium, phosphorus, tin, antimony, lead,vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium,preferably from the group constituted by aluminium, titanium, zirconium,niobium, germanium and gallium, more preferably aluminium. The presentinvention also concerns the preparation of the material of theinvention. A first process for preparing the material of the inventioncomprises a) synthesis, in the presence of a template, of zeoliticnanocrystals with a maximum nanometric dimension of 300 nm to obtain acolloidal solution in which said nanocrystals are dispersed; b) mixing,in solution, at least one surfactant, at least one silicic precursor,optionally at least one precursor of at least one element X selectedfrom the group constituted by aluminium, titanium, tungsten, zirconium,gallium, germanium, phosphorus, tin, antimony, lead, vanadium, iron,manganese, hafnium, niobium, tantalum and yttrium, and at least onecolloidal solution obtained in accordance with a); c) aerosolatomization of said solution obtained in step b) to result in theformation of spherical droplets with a diameter of less than 200 μm; d)drying said droplets; and e) eliminating said template and saidsurfactant to obtain a material with a hierarchical porosity. A secondprocess for preparing a material according to the invention comprisesa′) mixing, in solution, at least one surfactant, at least one silicicprecursor, optionally at least one precursor of at least one element Xselected from the group constituted by aluminium, titanium, tungsten,zirconium, gallium, germanium, phosphorus, tin, antimony, lead,vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium, andzeolitic crystals dispersing into the form of nanocrystals with amaximum nanometric dimension of 300 nm in said solution; b′) aerosolatomization of said solution obtained in step a′) to result in theformation of spherical droplets with a diameter of less than 200 μm; c′)drying said droplets; and d′) eliminating at least said surfactant. Theordered structure of the matrix of the material of the invention isconsecutive to the micellization or self-organization phenomenon byevaporation induced by the aerosol technique.

APPLICATION OF THE INVENTION

The material of the invention, which comprises a mesostructuredinorganic matrix based on silicon oxide, with amorphous walls in whichzeolitic nanocrystals are trapped, simultaneously presents thestructural, textural and acid-basic properties of materials from thezeolite class and of materials based on silicon oxide, more preciselymesostructured aluminosilicate materials. Manufacture on the nanometricscale of a composite material based on mesostructured silicon/zeolitesresults in a fortuitous combination of microporous and mesoporous zoneswithin the same spherical particle. Further, since the material of theinvention is constituted by spherical elementary particles, the diameterof said particles is advantageously 50 nm to 10 μm and preferably 50 to300 nm; the limited dimension of said particles and their homogeneousshape produces better diffusion of the reagents and reaction productsduring use of the material of the invention in potential industrialapplications compared with known prior art materials in the form ofelementary particles of non homogeneous shape, i.e. irregular, and withdimensions of much more than 500 nm. Further, the processes forpreparation of the material of the invention consist of interacting,preferably in an acid medium, at least one surfactant, ionic or nonionic, with at least one silicic precursor, at least one optionalprecursor of at least one element X selected from the group constitutedby aluminium, titanium, tungsten, zirconium, gallium, germanium,phosphorus, tin, antimony, lead, vanadium, iron, manganese, hafnium,niobium, tantalum and yttrium, preferably selected from the groupconstituted by aluminium, titanium, zirconium, niobium, germanium andgallium, and more preferably aluminium, and either at least onecolloidal solution in which zeolitic nanocrystals with a maximumnanometric dimension of 300 nm or zeolitic crystals dispersing into theform of nanocrystals with a maximum nanometric dimension of 300 nm in asolution, preferably acidic. Since the ordered structure of the materialis consecutive to the micellization or self-organization phenomenon byevaporation induced by the aerosol technique, it can readily producematerials with a hierarchical porosity without damaging the nature ofthe mesostructured form or that of the zeolitic phase and allowsoperation with a wide range of zeolite nanocrystals regardless of theirinitial synthesis processes. In fact, zeolitic crystals with dimensionsmuch greater than 300 nm can be used provided that they can disperse insolution, in particular in an acidic solution and more preferably in anhydro-organic acidic solution, in the form of nanocrystals with amaximum nanometric dimension of 300 nm. Further, compared with knownsyntheses for mesostructured aluminosilicates, production of thematerial of the invention is carried out continuously and thepreparation time is reduced (a few hours as opposed to 12 to 24 hours byautoclaving).

The materials produced in accordance with the invention can be usedconventionally in the processes disclosed in the references cited above,the disclosures of which are entirely incorporated by reference herein.

DISCLOSURE OF THE INVENTION

The present invention provides a material with a hierarchical porosity,constituted by at least two spherical elementary particles, each of saidspherical particles comprising zeolitic nanocrystals having a pore sizein the range 0.2 to 2 nm and a matrix based on silicon oxide, which ismesostructured, having a pore size in the range 1.5 to 30 nm and havingamorphous walls with a thickness in the range 1 to 20 nm, said sphericalelementary particles having a maximum diameter of 10 μm.

The term “hierarchical porosity material” as used in the presentinvention means a material having a double porosity on the scale of eachof said spherical particles: mesoporosity, i.e. a porosity organized onthe mesopore scale, having a uniform dimension in the range 2.5 to 30nm, preferably in the range 1.5 to 10 nm, distributed homogeneously andin a regular manner in each of said particles (mesostructuring), and azeolitic type microporosity the characteristics of which (zeolitestructure type, chemical composition of the zeolitic framework) are afunction of the choice of zeolitic nanocrystals. The material of theinvention also has an intraparticular textural macro porosity. It shouldbe noted that porosity of a microporous nature may also result frominsinuation of the surfactant used during preparation of the material ofthe invention, with the inorganic wall at the organic-inorganicinterface developed during mesostructuring of the inorganic component ofsaid material of the invention. In accordance with the invention, thezeolitic nanocrystals have a pore size in the range 0.2 to 2 nm,preferably in the range 0.2 to 1 nm and more preferably in the range 0.2to 0.6 nm. Said nanocrystals generate the microporosity in each of thespherical elementary particles constituting the material of theinvention.

The matrix based on silicon oxide included in each of the sphericalparticles constituting the material of the invention is mesostructured:it has mesopores having a uniform size in the range 1.5 to 30 nm andpreferably in the range 1.5 to 10 nm, distributed homogeneously andregularly in each of said particles. The material located between themesopores of each of said spherical particles is amorphous and formswalls the thickness of which is in the range 1 to 20 nm. The thicknessof the walls corresponds to the distance separating one pore fromanother pore. The organization of the mesoporosity described aboveresults in a structuration of the matrix based on silicon oxide, whichmay be hexagonal, vermicular or cubic, preferably vermicular.

In accordance with a particular implementation of the material of theinvention, the matrix based on silicon oxide, which is mesostructured,is entirely silicic. In accordance with a further particularimplementation of the material of the invention, the matrix based onsilicon oxide, which is mesostructured, further comprises at least oneelement X selected from the group constituted by aluminium, titanium,tungsten, zirconium, gallium, germanium, phosphorus, tin, antimony,lead, vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium,preferably from the group constituted by aluminium, titanium, zirconium,niobium, germanium and gallium, and more preferably aluminium.Preferably, the element X is aluminium: in this case the matrix of thematerial of the invention is an aluminosilicate. Said aluminosilicatehas a Si/Al molar ratio of at least 1, preferably in the range 1 to 1000and more preferably in the range 1 to 100.

According to the invention, the zeolitic nanocrystals advantageouslyrepresent 0.1% to 30% by weight, preferably 0.1% to 20% by weight andmore preferably 0.1% to 10% by weight of the material of the invention.Any zeolite is possible; in particular but not exhaustively, thoselisted in the “Atlas of zeolite framework types”, 5^(th) revisedEdition, 2001, Ch Baerlocher, W M Meier, D H Olson may be employed inthe zeolitic nanocrystals present in each of the spherical elementaryparticles constituting the material of the invention. The zeoliticnanocrystals preferably comprise at least one zeolite selected from thefollowing zeolites: ZSM-5, ZSM-48, ZSM-22, ZSM-23, ZBM-30, EU-2, EU-11,silicalite, beta, zeolite A, faujasite, Y, USY, VUSY, SDUSY, mordenite,NU-87, NU-88, NU-86, NU-85, IM-5, IM-12, ferrierite and EU-1. Morepreferably, the zeolitic nanocrystals comprise at least one zeoliteselected from zeolites with structure type MFI, BEA, FAU and LTA.Nanocrystals of different zeolites and in particular zeolites withdifferent structure types may be present in each of the sphericalparticles constituting the material of the invention. In particular,each of the spherical particles constituting the material of theinvention may advantageously comprise at least the first zeoliticnanocrystals the zeolite of which is selected from the followingzeolites: ZSM-5, ZSM-48, ZSM-22, ZSM-23, ZBM-30, EU-2, EU-11,silicalite, beta, zeolite A, faujasite, Y, USY, VUSY, SDUSY, mordenite,NU-87, NU-88, NU-86, NU-85, IM-5, IM-12, ferrierite and EU-1, preferablyfrom zeolites with structure type MFI, BEA, FAU and LTA, and at leastsecond zeolitic nanocrystals the zeolite of which is different from thatof the first zeolitic nanocrystals and is selected from the followingzeolites: ZSM-5, ZSM-48, ZSM-22, ZSM-23, ZBM-30, EU-2, EU-11,silicalite, beta, zeolite A, faujasite, Y, USY, VUSY, SDUSY, mordenite,NU-87, NU-88, NU-86, NU-85, IM-5, IM-12, ferrierite and EU-1, preferablyfrom zeolites with structure type MFI, BEA, FAU and LTA. Advantageously,the zeolitic nanocrystals comprise at least one zeolite which is eitherentirely silicic or, in addition to silicon, contains at least oneelement T selected from aluminium, iron, boron, indium and gallium,preferably aluminium.

In accordance with the invention, the diameter of said sphericalelementary particles constituting the material of the invention isadvantageously in the range 50 to 10 μm, preferably in the range 50 to300 nm. More precisely, they are present in the material of theinvention in the form of aggregates.

The material of the invention advantageously has a specific surface areain the range 100 to 1100 m²/g, more advantageously in the range 400 to800 m²/g.

The present invention also concerns the preparation of the material ofthe invention. It proposes two processes for preparing the material ofthe invention. A first implementation of the process for preparing thematerial of the invention, hereinafter termed the “first preparationprocess of the invention” comprises: a) synthesis, in the presence of atemplate, of zeolitic nanocrystals with a maximum nanometric dimensionof 300 nm to obtain a colloidal solution in which said nanocrystals aredispersed; b) mixing, in solution, at least one surfactant, at least onesilicic precursor, optionally at least one precursor of at least oneelement X selected from the group constituted by aluminium, titanium,tungsten, zirconium, gallium, germanium, phosphorus, tin, antimony,lead, vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium,and at least one colloidal solution obtained in accordance with a); c)aerosol atomization of said solution obtained in step b) to result inthe formation of spherical droplets with a diameter of less than 200 μm;d) drying said droplets; and e) eliminating said template and saidsurfactant to obtain a material with a hierarchical porosity.

In accordance with step a) of the first preparation process of theinvention, the zeolitic nanocrystals are synthesized using operatingprotocols which are known to the skilled person. In particular, thesynthesis of beta zeolite nanocrystals has been described by T Bein etal, Micropor Mesopor Mater, 2003, 64, 165. The synthesis of Y zeolitenanocrystals has been described by T J Pinnavaia et al, J Am Chem Soc,2000, 122, 8791. The synthesis of faujasite zeolite nanocrystals hasbeen described by Kloetstra et al, Microporous Mater, 1996, 6, 287; thesynthesis of ZSM-5 zeolite nanocrystals has been described by R Mokayaet al, J Mater Chem., 2004, 14, 863. The synthesis of silicalitenanocrystals (or of structure type MFI) has been described by R deRuiter et al, Synthesis of Microporous Materials, Vol I, M L Occelli, HE Robson (eds), Van Nostrand Reinhold, New York, 1992, 167 and is givenin Example 1 of the present application.

In general, zeolitic nanocrystals are synthesized by preparing areaction mixture comprising at least one silicon source, optionally atleast one source of at least one element T selected from aluminium,iron, boron, indium and gallium, preferably at least one source ofaluminium, and at least one template. The reaction mixture is eitheraqueous or hydro-organic, for example a water-alcohol mixture. Thereaction mixture is advantageously placed under hydrothermal conditionsunder autogenous pressure, optionally by adding a gas, for examplenitrogen, at a temperature in the range 50° C. to 200° C., preferably inthe range 60° C. to 170° C. and more preferably at a temperature whichdoes not exceed 120° C. until the zeolitic nanocrystals are formed. Atthe end of said hydrothermal treatment, a colloidal solution is obtainedin which the nanocrystals are in the dispersed state. The template maybe ionic or neutral depending on the zeolite to be synthesized. It isnormal to use templates from the following non exhaustive list:nitrogen-containing organic cations, elements from the alkalis (Cs, K,Na, etc), crown ethers, diamines and any other template which is wellknown to the skilled person.

In step b) of the first preparation process of the invention, element Xis preferably selected from the group formed by aluminium, titanium,zirconium, niobium, germanium and gallium; more preferably, X isaluminium.

In a second implementation of the process for preparing the material ofthe invention, hereinafter termed the “second preparation process of theinvention”, zeolitic crystals are initially used which have thecharacteristic of dispersing in the form of nanocrystals with a maximumnanometric dimension of 300 nm in solution, for example in acidichydro-organic solution. The second preparation process of the inventioncomprises a′) mixing, in solution, at least one surfactant, at least onesilicic precursor, optionally at least one precursor of at least oneelement X selected from the group constituted by aluminium, titanium,tungsten, zirconium, gallium, germanium, phosphorus, tin, antimony,lead, vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium,and zeolitic crystals dispersing into the form of nanocrystals with amaximum nanometric dimension of 300 nm in said solution; b′) aerosolatomization of said solution obtained in step a′) to result in theformation of spherical droplets with a diameter of less than 200 μm; c′)drying said droplets; and d′) eliminating at least said surfactant.

In step a′) of the second preparation process of the invention, zeoliticcrystals are used. Any crystalline zeolite which is known in the art andwhich has the property of dispersing in solution, for example in acidichydro-organic solution, in the form of nanocrystals with a maximumnanometric dimension of 300 nm. is suitable for carrying out step a′).Said zeolitic crystals are synthesized using methods which are known tothe skilled person. The zeolitic crystals used in step a′) may alreadybe in the form of nanocrystals. Zeolitic crystals with a dimension ofmore than 300 nm, for example in the range 300 nm to 200 μm can alsoadvantageously be used if they disperse in solution, for example inhydro-organic solution, preferably in acidic hydro-organic solution, inthe form of nanocrystals with a maximum nanometric dimension of 300 nm.Zeolitic crystals dispersing in the form of nanocrystals with a maximumnanometric dimension of 300 nm can also be obtained by functionalizationof the nanocrystal surface. The element X is preferably selected fromthe group constituted by aluminium, titanium, zirconium, niobium,germanium and gallium; more preferably, X is aluminium. The zeoliticcrystals used are either in their as synthesized form, i.e. stillcontaining template, or in their calcined form, i.e. free of saidtemplate. When the zeolitic crystals used are in their as synthesizedform, said template is eliminated during step d′) of the secondpreparation process of the invention.

According to the two processes for preparing the material of theinvention, the silicic precursor and optional precursor for at least oneelement X, preferably the aluminium precursor, used in step b) of thefirst preparation process of the invention, are precursors of inorganicoxides which are well known to the skilled person. The silicic precursoris obtained from any source of silicon and advantageously from a sodiumsilicate precursor with formula SiO₂, NaOH, from a chlorine-containingprecursor with formula SiCl₄, from an organometallic precursor withformula Si(OR)₄ in which R═H, methyl, ethyl or from a chloroalkoxideprecursor with formula Si(OR)_(4-x)Cl_(x) in which R═H, methyl, ethyl, xbeing in the range 0 to 4. The silicic precursor may also advantageouslybe an organometallic precursor with formula Si(OR)_(4-x)R′_(x) in whichR═H, methyl, ethyl and R′ is an alkyl chain or a functionalized alkylchain, for example a thiol, amino, β diketone or sulphonic acid group, xbeing in the range 0 to 4. the precursor for element X may be anycompound comprising the element X which can liberate said element insolution, for example in hydro-organic solution, preferably in acidichydro-organic solution, in the reactive form. In the preferred case inwhich X is aluminium, the aluminium precursor is advantageously aninorganic aluminium salt with formula ALZ₃, Z being a halogen or the NO₃group. Preferably, Z is chlorine. The aluminium precursor may also be anorganometallic precursor with formula Al(OR″)₃ in which R″=ethyl,isopropyl, b-butyl, s-butyl or t-butyl or a chelated precursor such asaluminium acetylacetonate (Al(CH₇O₂)₃). The aluminium precursor may alsobe an aluminium oxide or hydroxide.

The surfactant used to prepare the mixture of step b) of the firstpreparation process of the invention or step a′) of the secondpreparation process of the invention is an ionic or non ionic surfactantor a mixture of the two. Preferably, the ionic surfactant is selectedfrom phosphonium or ammonium ions, and more preferably from quaternaryammonium salts such as cetyltrimethyl ammonium bromide (CTAB).Preferably, the non ionic surfactant may be any copolymer having atleast two portions with different polarities endowing them withamphiphilic macromolecular properties. Said copolymers may be includedin the following non exhaustive list of copolymer classes: fluorinatedcopolymers (—[CH₂—CH₂—CH₂—CH₂O—CO—R1- in which R1=C₄F₉, C₈F₁₇, etc),biological copolymers such as poly amino acids (polylysine, alginates,etc), dendrimers, block copolymers constituted by chains ofpoly(alkylene oxide) and any other copolymer with an amphiphilic naturewhich is known to the skilled person (S Forster, M Antionnetti, AdvMater, 1998, 10, 195-217, S Forster, T Plantenberg, Angew Chem Int Ed,2002, 41, 688-714, H Colfen, Macromol Rapid Commun, 2001, 22, 219-252).

Preferably, in the context of the present invention, a block copolymerconstituted by poly (alkylene oxide) chains is used. Said blockcopolymer is preferably a block copolymer having two, three of fourblocks, each block being constituted by one poly(alkylene oxide) chain.For a two-block copolymer, one of the blocks is constituted by apoly(alkylene oxide) chain which is hydrophilic in nature and the otherblock is constituted by a poly(alkylene oxide) chain which ishydrophobic in nature. For a three-block copolymer, two of the blocksare constituted by a poly(alkylene oxide) chain which is hydrophilic innature while the other block, located between two blocks withhydrophilic portions, is constituted by a poly(alkylene oxide) chainwhich is hydrophobic in nature. Preferably, in the case of a three-blockcopolymer, the chains of poly(alkylene oxide) of hydrophilic nature arechains of poly(ethylene oxide), (PEO)_(x) and (PEO)_(z), and thepoly(alkylene oxide) chains which are hydrophobic in nature are chainsof poly (propylene oxide), (PPO)_(y), chains of poly(butylene oxide) ormixed chains, each chain of which is a mixture of several alkylene oxidemonomers. More preferably, in the case of a three-block copolymer, acompound with formula (PEO)_(x)(PPO)_(y)(PEO)_(z) is used in which x isin the range 5 to 106, y is in the range 33 to 70 and z is in the range5 to 106. Preferably, the values of x and z are identical. Highlyadvantageously, a compound in which x=20, y=70 and z=20 (P123) is usedand a compound in which x=106, y=70 and z=106 (F127) is used.Commercially available non ionic surfactants known as Pluronic (BASF),Tetronic (BASF), Triton (Sigma), Tergitol (UnionCarbide), Brij (Aldrich)can be used as non ionic surfactants in step b) of the first preparationprocess of the invention or in step a′) of the second process of theinvention. For a four-block copolymer, two of the blocks are constitutedby a poly(alkylene oxide) chain which is hydrophilic in nature and thetwo other blocks are constituted by a poly(alkylene oxide) chain whichis hydrophobic in nature.

The solution into which the following are mixed: at least one silicicprecursor, optionally at least one precursor of at least one element X,preferably an aluminium precursor, at least one surfactant and, in thecase of step b) of the first preparation process of the invention, thecolloidal solution in which said synthesized zeolitic nanocrystals aredispersed, or in the case of step a′) of the second preparation processof the invention, zeolitic crystals are dispersed in said solution inthe form of nanocrystals with a maximum nanometric dimension of 300 nm;may be acidic, neutral or basic. Preferably, said solution is acidic andhas a maximum pH of 2, more preferably in the range 0 to 2. Non limitingexamples of acids used to obtain an acidic solution with a maximum pH of2 are hydrochloric acid, sulphuric acid and nitric acid. Said solutionmay be aqueous or it may be a water-organic solvent mixture, the organicsolvent preferably being a polar solvent, in particular an alcohol,preferably ethanol. Said solution may also be practically organic,preferably practically alcoholic, the quantity of water being such thathydrolysis of the inorganic precursors is ensured (stoichiometricquantity). More preferably, said solution in which the following aremixed: at least one silicic precursor, optionally at least one precursorof at least one element X, preferably an aluminium precursor, at leastone surfactant and, in the case of step b) of the preparation process ofthe invention, the colloidal solution in which said synthesized zeoliticnanocrystals are dispersed, or in the case of step a′) of the secondpreparation process of the invention the zeolitic crystals are dispersedin said solution in the form of nanocrystals with a maximum nanometricdimension of 300 nm, is a hydro-organic acid mixture, more preferably anacidic water-alcohol mixture.

In the preferred case in which the matrix of the material of theinvention contains aluminium, the concentrations of silicic andaluminium precursors in step b) of the first preparation process of theinvention or in step a′) of the second preparation process of theinvention are defined by the molar ratio Si/Al, this being at leastequal to 1, preferably in the range 1 to 1000, and more preferably inthe range 1 to 100. The quantity of zeolitic nanocrystals dispersed inthe colloidal solution introduced during step b) of the firstpreparation process of the invention, or that of the zeolitic crystalsintroduced during step a′) of the second preparation process of theinvention is such that the zeolitic nanocrystals advantageouslyrepresent 0.1% to 30% by weight, preferably 0.1% to 20% by weight andmore preferably 0.1% to 10% by weight of the material of the invention.

The initial concentration of surfactant introduced into the mixture ofstep b) of the first preparation process of the invention or step a′) ofthe second preparation process of the invention is defined by c₀ whichis defined with respect to the critical micellar concentration (c_(mc))which is well known to the skilled person. The c_(mc) is the limitingconcentration beyond which self-arrangement of the molecules ofsurfactant in the solution occurs. The concentration c₀ may be lessthan, equal to or more than c_(mc), preferably less than c_(mc). In apreferred implementation of one or the other of the processes of theinvention, the concentration c₀ is less than the c_(mc) and saidsolution in step b) of the first preparation process of the invention orin step a′) of the second preparation process of the invention is anacidic water-alcohol acidic mixture.

The step for atomizing a mixture in step c) of the first preparationprocess of the invention or in step b′) of the second preparationprocess of the invention produces spherical droplets with a diameterwhich is preferably in the range 2 to 200 μm. The size distribution ofsaid droplets is of the log normal type. The aerosol generator used is acommercial model 3078 apparatus supplied by TSI. The solution isatomized into a chamber into which a vector gas is sent, an O₂/N₂mixture (dry air), at a pressure P of 1.5 bars. In step d) of the firstpreparation process of the invention, or in step c′) of the secondpreparation process of the invention, said droplets are dried. Drying iscarried out by transporting said droplets via the vector gas, the O₂/N₂mixture, in glass tubes, which results in progressive evaporation of thesolution, for example of the hydro-organic acid solution, and theproduction of spherical elementary particles. Drying is completed bypassing said particles into an oven the temperature of which can beadjusted, usually between temperatures of 50° C. to 600° C. andpreferably 80° C. to 400° C., the residence time for said particles inthe oven being of the order of 3 to 4 seconds. The particles are thenharvested in a filter and constitute the material of the invention. Apump placed at the end of the circuit routes the species into theexperimental aerosol device.

In the case in which the solution in step b) of the first preparationprocess of the invention or step a′) of the second preparation processof the invention is a water-organic solvent mixture, preferably acidic,it is essential during step b) of the preparation process of theinvention or step a′) of the second preparation process of the inventionthat the concentration of surfactant at the start of mesostructuring ofthe matrix is less than the critical micellar concentration so thatevaporation of said hydro-organic solution, preferably acidic, duringstep c) of the first preparation process of the invention or step b′) ofthe second preparation process of the invention using the aerosoltechnique induces a phenomenon of micellization or self-organizationleading to mesostructuring of the matrix of material of the inventionaround the zeolitic nanocrystals which remain unchanged in form and sizeduring steps c) and d) of the first preparation process of the inventionor b′) and c′) of the second preparation process of the invention. Whenc₀<c_(mc), mesostructuring of the matrix of the material of theinvention prepared using one of the processes described above followsprogressive concentration of the silicic precursor in each droplet, ofthe optional precursor for element X, preferably an aluminium precursor,and of the surfactant, until a concentration of surfactant c>c_(mc)results from evaporation of the hydro-organic solution, preferablyacidic.

In general, increasing the joint concentration of the silicic precursorand possibly of the precursor for element X, preferably an aluminiumprecursor, and the surfactant causes precipitation of the silicicprecursor and of the optional precursor for element X, preferably thealuminium precursor, around the self-organized surfactant and as aconsequence, structuration of the matrix of the material of theinvention. The inorganic/inorganic phase, organic/organic phase andorganic/inorganic phase interactions result in a self-organizationmechanism which is cooperative with hydrolysis/condensation of thesilicic precursor and optional precursor for the element X, preferablyan aluminium precursor, around the surfactant. During saidself-organizing phenomenon, the zeolitic nanocrystals are trapped in thematrix based on silicon oxide, mesostructured, comprised in each of thespherical elementary particles constituting the material of theinvention. The aerosol technique is particularly advantageous forcarrying out step c) of the first preparation process of the inventionor step b′) of the second preparation process of the invention toconstrain the reagents present in the initial solution to interacttogether, with no possible loss of material apart from the solvents,i.e. the solution, preferably the aqueous solution, preferably acidic,and optionally supplemented with a polar solvent, the totality of thesilicon, optional element X, and the zeolitic nanocrystals initiallypresent then being perfectly preserved throughout each of the processesof the invention instead of potentially being eliminated during thefiltering steps and washes encountered in conventional synthesisprocesses known to the skilled person. Drying the droplets in step d) ofthe first preparation process of the invention or in step c′) of thesecond preparation process of the invention is advantageously followedby passage through an oven at a temperature in the range 50° C. to 150°C. Elimination of the template and the surfactant in step e) of thefirst preparation process of the invention or elimination of at leastthe surfactant in step d′) of the second preparation process of theinvention to obtain the material of the invention with a hierarchicalporosity is advantageously carried out by chemical extraction or heattreatment and preferably by calcining in air within a temperature rangeof 300° C. to 1000° C. and more precisely in a range of 500° C. to 600°C. for a period of 1 to 24 hours and preferably for a period of 2 to 6hours.

The material with a hierarchical porosity of the present invention maybe obtained in the form of powder, beads, pellets, granules orextrudates, the forming operations being carried out using conventionaltechniques which are known to the skilled person. Preferably, thematerial with a hierarchical porosity of the invention is obtained inthe form of a powder which is constituted by spherical elementaryparticles having a maximum diameter of 10 μm, which facilitates anydiffusion of the reagents in the case of the use of a material of theinvention in a potential industrial application.

The material of the invention with a hierarchical porosity ischaracterized using several analytical techniques and in particular bysmall angle X ray diffraction (small angle XRD), large angle X raydiffraction (XRD), the nitrogen adsorption isotherm, transmissionelectron microscopy (TEM) and X ray fluorescence elementary analysis.

Large angle X ray diffraction (2θ in the range 5° to 70) can be used tocharacterize a crystalline solid defined by repetition of a unit cell onthe molecular scale. In the discussion below, X ray analysis is carriedout on a powder using a diffractometer operating in reflection equippedwith a back monochromator using the copper radiation line (wavelength1.5406 Ä). The peaks normally observed on diffractograms correspondingto a given value for the angle 2θ are associated with the interplanarspacings d_(hkl) which are characteristic of the structural symmetry ofthe material, (hkl being the Miller indices of the reciprocal lattice)by the Bragg relationship: 2d_(hkl)*sin(θ)=n*λ. This indexation allowsthe lattice parameters (a, b, c) of the framework to be determineddirectly. Thus, large angle XRD analysis is adapted to structuralcharacterization of zeolitic nanocrystals present in each of thespherical elementary particles constituting the material of theinvention. In particular, it provides access to the pore dimensions ofthe zeolitic nanocrystals. Using the same principle, the small angle Xray diffraction technique (values for angle 2θ in the range 0.5° and 3°)can characterize the periodicity on a nanocrystal scale generated by theorganized mesoporosity of the mesostructured matrix based on siliconoxide of the material of the invention. The value of the latticeparameters (a, b, c) is a function of the hexagonal, cubic or vermicularstructure obtained. As an example, the large or small angle X raydiffractograms of a material with a hierarchical porosity obtained usingone of the processes of the invention constituted by zeolitenanocrystals of type ZSM-5 (MFI) zeolite show the mesostructured matrixas being purely silicic and obtained using a particular block copolymer,poly(ethylene oxide)₁₀₆-poly(propylene oxide)₇₀-poly(ethyleneoxide)₁₀₆(PEO₁₀₆—PPO₇₀—PEO₁₀₆ or F127) respectively have thediffractogram associated with the Pnma (n° 62) symmetry group of ZSM-5zeolite at large angles and a correlation peak which is perfectlyresolved at small angles associated with the vermicular structure of themesostructured matrix which corresponds to a correlation distance dbetween pores. The angle obtained on the XRD diffractogram allows thecorrelation distance d to be deduced using Bragg's law: 2d*sin(θ)=n*λ.

The values for the lattice parameters a, b, c obtained for thecharacterization of zeolite nanocrystals agree with the values obtainedfor a ZSM-5 type zeolite (MFI) which is well known to the skilled person(“Collection of simulated XRD powder patterns for zeolites”, 4^(th)edition, 2001, M M J Treacy, J B Higgins).

Nitrogen adsorption isothermal analysis corresponding to the physicaladsorption of nitrogen molecules in the pores of the material onprogressively increasing the pressure at constant temperature providesinformation regarding the textural characteristics (pore diameter,porosity type, specific surface area) which are peculiar to the materialof the invention. In particular, it provides access to the specificsurface area and to the mesoporous distribution of the material. Theterm “specific surface area” means the BET specific surface area(S_(BET) in m²/g) determined by nitrogen adsorption in accordance withAmerican standard ASTM D 3663-78 established using theBRUNAUER-EMMETT-TELLER method described in the periodical “The Journalof the American Society”, 60, 309, (1938). The pore distributionrepresentative of a population of mesopores centered in a range of 1.5to 50 nm is determined using the Barrett-Joyner-Halenda (BJH) model. Thenitrogen adsorption-desorption isotherm using the BJH model is describedin the periodical “The Journal of the American Society”, 73, 373 (1951)written by E P Barrett, L G Joyner and P P Halenda. In the descriptionbelow, the mesopore diameter φ in a given mesostructured matrixcorresponds to the mean diameter for nitrogen desorption defined as adiameter such that all pores with less than that diameter constitute 50%of the pore volume (Vp) measured on the desorption arm of the nitrogenisotherm. Further, the shape of the nitrogen adsorption isotherm and thehysteresis loop provides information regarding the presence ofmicroporosity linked to zeolitic nanocrystals and to the nature of themesoporosity. As an example, the nitrogen adsorption isotherm of amaterial with a hierarchical porosity obtained using one or other of theprocesses of the invention constituted by zeolite nanocrystals of theZSM-5 type (MFI), the mesostructured matrix being purely silicic andobtained using a particular block copolymer, poly(ethyleneoxide)₁₀₆-poly(propylene oxide)₇₀-poly(ethyleneoxide)₁₀₆(PEO₁₀₆—PPO₇₀—PEO₁₀₆ or F127) has, for low values of P/Po (inwhich Po is the saturated vapour pressure at temperature T), a type Iisotherm characteristic of a microporous material, and for higher valuesof P/Po, a type IV isotherm and a type H1 hysteresis loop, theassociated pore distribution curve being representative of a populationof mesopores with a uniform size centered in a range of 1.5 to 50 nm.Regarding the mesostructured matrix, the difference between the valuefor the pore diameter φ and the correlation distance between pores ddefined by small angle XRD as described above provides access to thedimension e in which e=d−φ and is characteristic of the thickness of theamorphous walls of the mesostructured matrix of the invention.

Transmission electron microscope analysis (TEM) is a technique which isalso widely used to characterize the mesostructured matrix of thematerial of the invention. This allows the formation of an image of thesolid being studied, the contrasts observed being characteristic of thestructural organization, texture or morphology of thezeolite/mesostructure composition of the particles observed, theresolution reaching a maximum of 0.2 nm. In the description below, TEMimages were produced from microtomed sections of the sample to visualizea section of a spherical elementary particle of the material of theinvention. As an example, TEM images obtained for an aluminosilicatematerial with a hierarchical porosity obtained using one or other of theprocesses of the invention constituted by type ZSM-5 zeolitenanocrystals (MFI), the mesostructured matrix being purely silicic andobtained using a particular block copolymer, F127, had a vermicularmesostructure within the same spherical particle (the material beingdefined by the dark zones) within which can be seen substantiallyspherical opaque objects representing the zeolitic nanocrystals trappedin the mesostructured matrix. Analysis of the image also provides accessto the parameters d, φ and e, characteristic of the mesostructuredmatrix defined above. It is also possible to visualize on the samerecord the lattice planes of the nanocrystals instead of the opaqueobjects mentioned above and thus to deduce the structure of the zeolite.

The morphology and dimensional distribution of the elementary particleswere established from analysis of the images obtained by SEM (scanningelectron microscopy).

The structure of the mesostructured material of the invention may be ofthe vermicular, cubic or hexagonal type depending on the nature of thesurfactant selected as the template.

The invention will now be illustrated by the following examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a diffractogram of ZSM-5.

FIG. 2 represents a small angle XRD of a material of the invention.

FIG. 3 represents a large angle XRD of a material of the invention.

FIG. 4 represents a TEM analysis of a material of the invention.

FIG. 5 represents small and large angle XRD of a material of theinvention.

EXAMPLES

In the examples below, the aerosol technique used was that describedabove in the description of the invention.

Example 1 (Invention) Preparation of Material with a HierarchicalPorosity Constituted by Zeolite Nanocrystals of the Silicalite Type(MFI) in an Amount of 3.7% of the Final Material Weight and a PurelySilicic Mesostructured Matrix

6.0 g of TEOS (tetraethylorthosilicate) was hydrolyzed in 10.4 ml oftetrapropyl ammonium hydroxide (TPAOH, 20%). 1.5 ml of water was thenadded and the solution was stirred to obtain a clear solution. Thesolution was autoclaved at T=80° C. for 4 days. Once synthesis wascomplete, the crystals were recovered by centrifuging (20000 rpm for onehour), re-dispersed in water (ultrasound) then re-centrifuged until thesolution after re-dispersion had a pH of close to 7. The pH of thecolloidal suspension of silicalite-1 nanocrystals was then adjusted to9.5 by adding a 0.1% ammoniacal solution. The mean silicalite crystalsize was 100 nm. 400 μl of said solution was then added to a solutioncontaining 30 g of ethanol, 15 ml of water, 4.5 g of TEOS, 0.036 ml ofHCl and 1.4 g of F127 surfactant. The pH of the solution was adjusted to2. The ensemble was sent to the atomization chamber of an aerosolgenerator as described above and the solution was atomized in the formof fine droplets under the action of the vector gas (dry air) introducedunder pressure (P=1.5 bars). The droplets were dried using the protocoldescribed in the invention described above. The temperature of thedrying oven was fixed at 350° C. The harvested powder was then calcinedin air for 5 h at T=550° C. The solid was characterized by small angleand large angle XRD, by the nitrogen adsorption isotherm, by TEM and byX ray fluorescence. TEM analysis showed that the final material wasconstituted by silicalite zeolite nanocrystals trapped in a purelysilicic matrix with an organized mesoporosity characterized by avermicular structure. The nitrogen adsorption isothermal analysisproduced a specific surface area in the final material of S_(BET)=480m²/g and a mesopore diameter characteristic of the purely silicicmesostructured matrix of φ=6.2 nm. Large angle XRD produced adiffractogram characteristic of silicalite zeolite (micropore dimension,measured by XRD, of the order of 0.55 nm). Small angle XRD showed acorrelation peak associated with a vermicular organization of themesostructured matrix. The Bragg relationship, 2d*sin(0.3)=1.5406, gaved=15 nm. The thickness of the amorphous walls of the purely silicicmesostructured matrix defined by e=d−φ was thus e=9 nm. A SEM image ofthe spherical elementary particles obtained indicated that the particlesize was characterized by a diameter of 50 to 700 nm, with a particlesize distribution being centred around 300 nm.

Example 2 (Invention) Preparation of Material with a HierarchicalPorosity Constituted by Zeolite Nanocrystals of the ZSM-5 Type (MFI) inan Amount of 3.7% of the Final Material Weight and a Purely SilicicMesostructured Matrix

0.14 g of aluminium sec-butoxide was added to a solution containing 7 gof tetrapropyl ammonium hydroxide solution (TPAOH, 20%), 4.3 ml of waterand 0.0092 g of sodium hydroxide. 6 g of TEOS (tetraethylorthosilicate)was then added to this solution which was stirred at ambient temperatureto obtain a clear solution. The solution was placed in an oven at T=95°C. for 18 hours. A milky white colloidal suspension was obtainedcontaining ZSM-5 zeolite nanocrystals with a mean dimension of 130 nm.FIG. 1 shows a diffractogram of ZSM-5 nanocrystals. 400 μl of saidsolution was then added to a solution containing 30 g of ethanol, 15 mlof water, 4.5 g of TEOS, 0.036 ml of HCl and 1.4 g of F127 surfactant.The pH of the solution was adjusted to 2 with HCl. The ensemble was sentto the atomization chamber of an aerosol generator as described aboveand the solution was atomized in the form of fine droplets under theaction of the vector gas (dry air) introduced under pressure (P=1.5bars) as described above. The droplets were dried using the protocoldescribed in the invention described above. The temperature of thedrying oven was fixed at 350° C. The harvested powder was then calcinedin air for 5 h at T=550° C. The solid was characterized by small angle(FIG. 2) and large angle (FIG. 3) XRD, by the nitrogen adsorptionisotherm, by TEM and by X ray fluorescence. TEM analysis (FIG. 4) showedthat the final material was constituted by nanocrystals of ZSM-5 zeolitetrapped in a purely silicic matrix with an organized mesoporositycharacterized by a vermicular structure. The nitrogen adsorptionisothermal analysis produced a specific surface area in the finalmaterial of S_(BET)=480 m²/g and a mesopore diameter characteristic ofthe purely silicic mesostructured matrix of φ=6.2 nm. Large angle XRDproduced a diffractogram characteristic of ZSM-5 zeolite (microporedimension, measured by XRD, of the order of 0.55 nm). Small angle XRDshowed a correlation peak associated with a vermicular organization ofthe mesostructured matrix. The Bragg relationship, 2d*sin(0.3)=1.5406,gave d=15 nm. The thickness of the amorphous walls of the purely silicicmesostructured matrix defined by e=d−φ was thus e=9 nm. A SEM image ofthe spherical elementary particles obtained indicated that the particlesize was characterized by a diameter of 50 to 700 nm, with a particlesize distribution being centred around 300 nm.

Example 3 (Invention) Preparation of an Aluminosilicate Material with aHierarchical Porosity Constituted by Zeolite Nanocrystals of the ZSM-5Type (MFI) (Si/Al=50) in an Amount of 10% of the Final Material Weightand a Aluminosilicate Mesostructured Matrix (Si/Al=4)

0.14 g of aluminium tri-sec-butoxide was added to a solution containing3.5 ml of TPAOH, 0.01 g of sodium hydroxide NaOH and 4.3 ml of water.After dissolving the aluminium alkoxide, 6 g of TEOS(tetraethylorthosilicate) was added. The solution was stirred at ambienttemperature for 5 hours and autoclaved at T=95° C. for 12 h. The whitesolution obtained contained 135 nm ZSM-5 nanocrystals. The solution wascentrifuged at 20000 rpm for 30 minutes. The solid was redispersed inwater then centrifuged again at 20000 rpm for 30 minutes. This washingwas carried out twice. The nanocrystals formed a gel which was ovendried overnight at 60° C. 0.461 g of these crystals was redispersed in asolution containing 30 g of ethanol, 15 ml of water, 3.59 g of TEOS,1.03 g of AlCl₃.6H₂O, 0.036 ml of HCl and 1.4 g of P123 surfactant byultrasound agitation for 24 hours. The ensemble was sent to theatomization chamber of an aerosol generator as described above and thesolution was atomized in the form of fine droplets under the action ofthe vector gas (dry air) introduced under pressure (P=1.5 bars) usingthe method described above. The droplets were dried using the protocoldescribed in the invention described above. The temperature of thedrying oven was fixed at 350° C. The harvested powder was then calcinedin air for 5 h at T=550° C. The solid was characterized by small angleand large angle (FIG. 5) XRD, by the nitrogen adsorption isotherm, byTEM and by X ray fluorescence. TEM analysis showed that the finalmaterial was constituted by nanocrystals of ZSM-5 zeolite trapped in apurely silicic matrix with an organized mesoporosity characterized by avermicular structure. The nitrogen adsorption isothermal analysisproduced a specific surface area in the final material of S_(BET)=478m²/g and a mesopore diameter characteristic of the mesostructuredaluminosilicate matrix of φ=4 nm. Large angle XRD produced adiffractogram characteristic of ZSM-5 zeolite (micropore dimension ofthe order of 0.55 nm). Small angle XRD showed a correlation peakassociated with a vermicular organization of the mesostructured matrix.The Bragg relationship, 2d*sin(0.4)=1.5406, gave d=11 nm. The thicknessof the amorphous walls of the aluninosilicate mesostructured matrixdefined by e=d−φ was thus e=7 nm. A SEM image of the sphericalelementary particles obtained indicated that the particle size wascharacterized by a diameter of 50 to 700 nm, with a particle sizedistribution being centred around 300 nm.

Example 4 (Invention) Preparation of an Aluminosilicate Material with aHierarchical Porosity Constituted by Type A Zeolite Nanocrystals (LTA)(Si/Al=6) in an Amount of 3.7% of the Final Material Weight and a PurelySilicic Mesostructured Matrix

2.19 g of aluminium isopropoxide was added to a solution containing 3.5ml of tetramethyl ammonium hydroxide (TMAOH), 0.01 g of sodium hydroxideNaOH and 28 ml of water. After dissolving the aluminium alkoxide, 6 g ofTEOS (tetraethylorthosilicate) was added. The solution was stirred atambient temperature for 5 hours and autoclaved at T=95° C. for 12 h. Thewhite solution obtained contained 140 nm LTA nanocrystals. 400 μl ofthis solution was then added to a solution containing 30 g of ethanol,15 ml of water, 4.5 g of TEOS, 0.036 ml of HCl and 1.4 g of F127surfactant. The pH of the solution was adjusted to 2. The ensemble wassent to the atomization chamber of an aerosol generator and the solutionwas atomized in the form of fine droplets under the action of the vectorgas (dry air) introduced under pressure (P=1.5 bars) using the methoddescribed above. The droplets were dried using the protocol described inthe invention described above. The temperature of the drying oven wasfixed at 350° C. The harvested powder was then calcined in air for 5 hat T=550° C. The solid was characterized by small angle and large angleXRD, by the nitrogen adsorption isotherm, by TEM and by X rayfluorescence. TEM analysis showed that the final material wasconstituted by nanocrystals of type A zeolite trapped in a purelysilicic matrix with an organized mesoporosity characterized by avermicular structure. The nitrogen adsorption isothermal analysisproduced a specific surface area in the final material of S_(BET)=478m²/g and a mesopore diameter characteristic of the purely silicicmesostructured matrix of φ=6 nm. Large angle XRD produced adiffractogram characteristic of LTA zeolite. Small angle XRD showed acorrelation peak associated with a vermicular organization of theporosity. The Bragg relationship, 2d*sin(0.3)=1.5406, gave d=15 nm. Thethickness of the amorphous walls of the purely silicic mesostructuredmatrix defined by e=d−φ was thus e=9 nm. A SEM image of the sphericalelementary particles obtained indicated that the particle size wascharacterized by a diameter of 50 to 700 nm, with a particle sizedistribution being centred around 300 nm.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosure of all applications, patents and publications,cited herein and of corresponding French application No. 0406940, filedJun. 24, 2004 is incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A material with a hierarchical porosity, constituted by at least twospherical elementary particles, each of said spherical particlescomprising zeolitic nanocrystals having a pore size in the range 0.2 to2 nm and a matrix based on silicon oxide, which is mesostructured,having a pore size in the range 1.5 to 30 nm and having amorphous wallswith a thickness in the range 1 to 20 nm, said spherical elementaryparticles having a maximum diameter of 10 μm.
 2. A material according toclaim 1, in which said zeolitic nanocrystals have a pore dimension inthe range 0.2 to 0.6 nm.
 3. A material according to claim 1, in whichthe pore size of said mesostructured matrix is in the range 1.5 to 10nm.
 4. A material according to claim 1, in which said mesostructuredmatrix has a hexagonal, cubic or vermicular structure.
 5. A materialaccording to claim 1, in which said matrix based on silicon oxide isentirely silicic.
 6. A material according to claim 1, in which saidmatrix based on silicon oxide comprises at least one element X selectedfrom the group constituted by aluminium, titanium, zirconium, gallium,germanium and niobium.
 7. A material according to claim 6, in which theelement X is aluminium.
 8. A material according to claim 7, in whichsaid matrix has a Si/Al ratio of at least
 1. 9. A material according toclaim 1, in which the zeolitic nanocrystals comprise at least onezeolite selected from zeolites with structure type MFI, BEA, FAU andLTA.
 10. A material according to claim 1, in which said zeoliticnanocrystals comprise at least one entirely silicic zeolite.
 11. Amaterial according to claim 1, in which said zeolitic nanocrystalscomprise at least one zeolite containing silicon and aluminium.
 12. Amaterial according to claim 1, with a specific surface area in the range100 to 1100 m²/g.
 13. A process for preparing a material according toclaim 1, comprising a) synthesis, in the presence of a template, ofzeolitic nanocrystals with a maximum nanometric dimension of 300 nm toobtain a colloidal solution in which said nanocrystals are dispersed; b)mixing, in solution, at least one surfactant, at least one silicicprecursor, optionally at least one precursor of at least one element Xselected from the group constituted by aluminium, titanium, tungsten,zirconium, gallium, germanium, phosphorus, tin, antimony, lead,vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium, andat least one colloidal solution obtained in accordance with a); c)aerosol atomization of said solution obtained in step b) to result inthe formation of spherical droplets with a diameter of less than 200 μm;d) drying said droplets; and e) eliminating said template and saidsurfactant to obtain a material with a hierarchical porosity.
 14. Aprocess for preparing a material according to claim 1, comprising a′)mixing, in solution, at least one surfactant, at least one silicicprecursor, optionally at least one precursor of at least one element Xselected from the group constituted by aluminium, titanium, tungsten,zirconium, gallium, germanium, phosphorus, tin, antimony, lead,vanadium, iron, manganese, hafnium, niobium, tantalum and yttrium, andzeolitic crystals dispersing into the form of nanocrystals with amaximum nanometric dimension of 300 nm in said solution; b′) aerosolatomization of said solution obtained in step a′) to result in theformation of spherical droplets with a diameter of less than 200 μm; c′)drying said droplets; and d′) eliminating at least said surfactant. 15.A process according to claim 13, in which the element X is aluminium.16. A process according to claim 13, in which said surfactant is a threeblock copolymer, each block being constituted by a poly(alkylene oxide)chain.
 17. A process according to claim 16, in which said three-blockcopolymer is constituted by two chains of poly(ethylene oxide) and onechain of poly(propylene oxide).